1. Field of the Invention
The present invention concerns a circuit for connection of at least two signal sources with at least one signal output, the signal sources being connected to a control unit that activates or deactivates the signal sources via transmission of control signals.
2. Description of the Prior Art
In the transmission of electrical signals from signal sources to a signal output that, for example, is connected to a signal evaluation unit, it is frequently necessary to selectively connect a number of signal sources with only one signal evaluation unit. This is in particular the case in magnetic resonance apparatuses where it is necessary to connect a large number of surface coils with a lesser number of preamplifiers. It is additionally necessary that only a few or only one single surface coil are/is active at the same time in order to prevent crosstalk from the other surface coils. The large number of surface coils is, for example, advantageous when a larger region of a patient is to be examined without intrusion into the examination space. The use of larger coils is disadvantageous because, in this case, the signal-to-noise ratio is significantly smaller in comparison to smaller coils. In most magnetic resonance apparatuses, the number of the preamplifiers that are connected with the surface coils is the limiting factor for the number of usable surface coils. Should a large number of smaller coils be used, these must be selectively connected with the preamplifier inputs.
A circuit is known from U.S. Pat. No. 6,677,755 by means of which a number of coils can be connected with preamplifiers of a magnetic resonance apparatus. For this purpose, a switching matrix composed of radio-frequency switches is controlled via a control line by a switch controller, so the coils can be selectively connected with the preamplifiers. The coils can be activated or deactivated by a coil control unit. A disadvantage of this known circuit is its high circuit complexity.